Local Electrochemical Co‐Sintering Enables Stable High‐Loading All‐Solid‐State Silicon Anodes in Li‐Ion Batteries

ABSTRACT Silicon anodes are promising for all‐solid‐state batteries (ASSBs) due to their high specific capacity and dendrite‐free safety. However, its practical application is hindered by a fundamental trade‐off: pure silicon anodes suffer from poor transport kinetics, while composite silicon anodes, designed to improve transport, face severe interfacial passivation from the decomposition of solid electrolytes. Here, we introduce a local electrochemical co‐sintering (LECS) strategy to resolve this dilemma. This is achieved through a counter‐intuitive positive silicon gradient architecture, which harnesses (de)alloying stress to trigger localized silicon sintering toward the critical silicon/electrolyte interface. This in situ process encapsulates conductive additives within newly formed, densified silicon phases, simultaneously minimizing the reactive interface to suppress electrolyte decomposition and creating robust electronic pathways. As a result, the LECS anode demonstrates significantly enhanced kinetics and reversibility under high areal loading (over 4 mAh cm −2 ). This work establishes a paradigm of proactively engineering the electrode microstructure to achieve stable high‐energy ASSBs.